Enumerable.ToLookup 方法

参考

定义

命名空间:: System.Linq

程序集:: System.Linq.dll

程序集:: System.Core.dll

程序集:: netstandard.dll

重要

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从 IEnumerable<T> 生成一个泛型 Lookup<TKey,TElement>。

重载

ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>)	根据指定的键选择器和元素选择器函数，从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>。
ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>)	根据指定的键选择器函数、比较器和元素选择器函数，从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>。
ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>)	根据指定的键选择器函数和键比较器，从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>。
ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>)	根据指定的键选择器函数，从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>。

ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>)

Source:: Lookup.cs

Source:: Lookup.cs

Source:: Lookup.cs

根据指定的键选择器和元素选择器函数，从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>。

public:
generic <typename TSource, typename TKey, typename TElement>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::ILookup<TKey, TElement> ^ ToLookup(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, Func<TSource, TElement> ^ elementSelector);

public static System.Linq.ILookup<TKey,TElement> ToLookup<TSource,TKey,TElement> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, Func<TSource,TElement> elementSelector);

static member ToLookup : seq<'Source> * Func<'Source, 'Key> * Func<'Source, 'Element> -> System.Linq.ILookup<'Key, 'Element>

<Extension()>
Public Function ToLookup(Of TSource, TKey, TElement) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), elementSelector As Func(Of TSource, TElement)) As ILookup(Of TKey, TElement)

类型参数

TSource

source 的元素类型。

TKey

keySelector 返回的键的类型。

TElement

elementSelector 返回的值的类型。

参数

source: IEnumerable<TSource>

要从其创建 Lookup<TKey,TElement> 的 IEnumerable<T>。

keySelector: Func<TSource,TKey>

用于从每个元素中提取键的函数。

elementSelector: Func<TSource,TElement>

用于从每个元素产生结果元素值的转换函数。

ILookup<TKey,TElement>

一个包含从输入序列中选择的类型为 TElement 的值的 Lookup<TKey,TElement>。

例外

ArgumentNullException

source、keySelector 或 elementSelector 为 null。

示例

下面的代码示例演示如何使用 ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) 键选择器函数和元素选择器函数创建 Lookup<TKey,TElement> 。

class Package
{
    public string Company { get; set; }
    public double Weight { get; set; }
    public long TrackingNumber { get; set; }
}

public static void ToLookupEx1()
{
    // Create a list of Packages.
    List<Package> packages =
        new List<Package>
            { new Package { Company = "Coho Vineyard",
                  Weight = 25.2, TrackingNumber = 89453312L },
              new Package { Company = "Lucerne Publishing",
                  Weight = 18.7, TrackingNumber = 89112755L },
              new Package { Company = "Wingtip Toys",
                  Weight = 6.0, TrackingNumber = 299456122L },
              new Package { Company = "Contoso Pharmaceuticals",
                  Weight = 9.3, TrackingNumber = 670053128L },
              new Package { Company = "Wide World Importers",
                  Weight = 33.8, TrackingNumber = 4665518773L } };

    // Create a Lookup to organize the packages.
    // Use the first character of Company as the key value.
    // Select Company appended to TrackingNumber
    // as the element values of the Lookup.
    ILookup<char, string> lookup =
        packages
        .ToLookup(p => p.Company[0],
                  p => p.Company + " " + p.TrackingNumber);

    // Iterate through each IGrouping in the Lookup.
    foreach (IGrouping<char, string> packageGroup in lookup)
    {
        // Print the key value of the IGrouping.
        Console.WriteLine(packageGroup.Key);
        // Iterate through each value in the
        // IGrouping and print its value.
        foreach (string str in packageGroup)
            Console.WriteLine("    {0}", str);
    }
}

/*
 This code produces the following output:

 C
     Coho Vineyard 89453312
     Contoso Pharmaceuticals 670053128
 L
     Lucerne Publishing 89112755
 W
     Wingtip Toys 299456122
     Wide World Importers 4665518773
*/

Structure Package
    Public Company As String
    Public Weight As Double
    Public TrackingNumber As Long
End Structure

Sub ToLookupEx1()
    ' Create a list of Packages.
    Dim packages As New List(Of Package)(New Package() _
     {New Package With
      {.Company = "Coho Vineyard", .Weight = 25.2, .TrackingNumber = 89453312L},
      New Package With
      {.Company = "Lucerne Publishing", .Weight = 18.7, .TrackingNumber = 89112755L},
      New Package With
      {.Company = "Wingtip Toys", .Weight = 6.0, .TrackingNumber = 299456122L},
      New Package With
      {.Company = "Contoso Pharmaceuticals", .Weight = 9.3, .TrackingNumber = 670053128L},
      New Package With
      {.Company = "Wide World Importers", .Weight = 33.8, .TrackingNumber = 4665518773L}})

    ' Create a Lookup to organize the packages.
    ' Use the first character of Company as the key value.
    ' Select Company appended to TrackingNumber
    ' as the element values of the Lookup.
    Dim lookup As ILookup(Of Char, String) =
    packages.ToLookup(Function(p) _
                          Convert.ToChar(p.Company.Substring(0, 1)),
                      Function(p) _
                          p.Company & " " & p.TrackingNumber)

    Dim output As New System.Text.StringBuilder

    ' Iterate through each IGrouping in the Lookup.
    For Each packageGroup As IGrouping(Of Char, String) In lookup
        ' Print the key value of the IGrouping.
        output.AppendLine(packageGroup.Key)
        ' Iterate through each value in the IGrouping and print its value.
        For Each str As String In packageGroup
            output.AppendLine("   " & str)
        Next
    Next

    ' Select a group of packages by indexing directly into the Lookup.
    Dim cgroup As IEnumerable(Of String) = lookup("C"c)

    output.AppendLine(vbCrLf & "Packages from Company names that start with 'C':")
    For Each str As String In cgroup
        output.AppendLine(str)
    Next

    ' Display the output.
    Console.WriteLine(output.ToString())
End Sub

' This code produces the following output:
'
' C
'    Coho Vineyard 89453312
'    Contoso Pharmaceuticals 670053128
' L
'    Lucerne Publishing 89112755
' W
'    Wingtip Toys 299456122
'    Wide World Importers 4665518773
'
' Packages from Company names that start with 'C':
' Coho Vineyard 89453312
' Contoso Pharmaceuticals 670053128

注解

方法 ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) 返回， Lookup<TKey,TElement>一个一对多字典，用于将键映射到值的集合。不同于 Lookup<TKey,TElement> ， Dictionary<TKey,TValue>后者执行键到单个值的一对一映射。

默认相等比较器 Default 用于比较键。

适用于

ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>)

Source:: Lookup.cs

Source:: Lookup.cs

Source:: Lookup.cs

根据指定的键选择器函数、比较器和元素选择器函数，从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>。

public:
generic <typename TSource, typename TKey, typename TElement>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::ILookup<TKey, TElement> ^ ToLookup(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, Func<TSource, TElement> ^ elementSelector, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);

public static System.Linq.ILookup<TKey,TElement> ToLookup<TSource,TKey,TElement> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, Func<TSource,TElement> elementSelector, System.Collections.Generic.IEqualityComparer<TKey> comparer);

public static System.Linq.ILookup<TKey,TElement> ToLookup<TSource,TKey,TElement> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, Func<TSource,TElement> elementSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer);

static member ToLookup : seq<'Source> * Func<'Source, 'Key> * Func<'Source, 'Element> * System.Collections.Generic.IEqualityComparer<'Key> -> System.Linq.ILookup<'Key, 'Element>

<Extension()>
Public Function ToLookup(Of TSource, TKey, TElement) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), elementSelector As Func(Of TSource, TElement), comparer As IEqualityComparer(Of TKey)) As ILookup(Of TKey, TElement)

类型参数

TSource

source 的元素类型。

TKey

keySelector 返回的键的类型。

TElement

elementSelector 返回的值的类型。

参数

source: IEnumerable<TSource>

要从其创建 Lookup<TKey,TElement> 的 IEnumerable<T>。

keySelector: Func<TSource,TKey>

用于从每个元素中提取键的函数。

elementSelector: Func<TSource,TElement>

用于从每个元素产生结果元素值的转换函数。

comparer: IEqualityComparer<TKey>

用于比较键的 IEqualityComparer<T>。

ILookup<TKey,TElement>

一个包含从输入序列中选择的类型为 TElement 的值的 Lookup<TKey,TElement>。

例外

ArgumentNullException

source、keySelector 或 elementSelector 为 null。

注解

方法 ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>) 返回， Lookup<TKey,TElement>一个一对多字典，用于将键映射到值的集合。不同于 Lookup<TKey,TElement> ， Dictionary<TKey,TValue>后者执行键到单个值的一对一映射。

如果 comparer 为 null，则使用默认相等比较器 Default 来比较键。

适用于

ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>)

Source:: Lookup.cs

Source:: Lookup.cs

Source:: Lookup.cs

根据指定的键选择器函数和键比较器，从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>。

public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::ILookup<TKey, TSource> ^ ToLookup(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);

public static System.Linq.ILookup<TKey,TSource> ToLookup<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, System.Collections.Generic.IEqualityComparer<TKey> comparer);

public static System.Linq.ILookup<TKey,TSource> ToLookup<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer);

static member ToLookup : seq<'Source> * Func<'Source, 'Key> * System.Collections.Generic.IEqualityComparer<'Key> -> System.Linq.ILookup<'Key, 'Source>

<Extension()>
Public Function ToLookup(Of TSource, TKey) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), comparer As IEqualityComparer(Of TKey)) As ILookup(Of TKey, TSource)

类型参数

TSource

source 的元素类型。

TKey

keySelector 返回的键的类型。

参数

source: IEnumerable<TSource>

要从其创建 Lookup<TKey,TElement> 的 IEnumerable<T>。

keySelector: Func<TSource,TKey>

用于从每个元素中提取键的函数。

comparer: IEqualityComparer<TKey>

用于比较键的 IEqualityComparer<T>。

ILookup<TKey,TSource>

一个包含键和值的 Lookup<TKey,TElement>。每个组中的值顺序与 source 中的顺序相同。

例外

ArgumentNullException

source 或 keySelector 为 null。

注解

方法 ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>) 返回， Lookup<TKey,TElement>一个一对多字典，用于将键映射到值的集合。不同于 Lookup<TKey,TElement>Dictionary<TKey,TValue>，后者执行键到单个值的一对一映射。

如果 comparer 为 null，则使用默认相等比较器 Default 来比较键。

适用于

ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>)

Source:: Lookup.cs

Source:: Lookup.cs

Source:: Lookup.cs

根据指定的键选择器函数，从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>。

public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::ILookup<TKey, TSource> ^ ToLookup(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector);

public static System.Linq.ILookup<TKey,TSource> ToLookup<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector);

static member ToLookup : seq<'Source> * Func<'Source, 'Key> -> System.Linq.ILookup<'Key, 'Source>

<Extension()>
Public Function ToLookup(Of TSource, TKey) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey)) As ILookup(Of TKey, TSource)

类型参数

TSource

source 的元素类型。

TKey

keySelector 返回的键的类型。

参数

source: IEnumerable<TSource>

要从其创建 Lookup<TKey,TElement> 的 IEnumerable<T>。

keySelector: Func<TSource,TKey>

用于从每个元素中提取键的函数。

ILookup<TKey,TSource>

一个包含键和值的 Lookup<TKey,TElement>。每个组中的值顺序与 source 中的顺序相同。

例外

ArgumentNullException

source 或 keySelector 为 null。

注解

方法 ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>) 返回， Lookup<TKey,TElement>一个一对多字典，用于将键映射到值的集合。不同于 Lookup<TKey,TElement> ， Dictionary<TKey,TValue>后者执行键到单个值的一对一映射。

默认相等比较器 Default 用于比较键。

适用于

通过

Enumerable.ToLookup 方法

定义

重载

ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>)

类型参数

参数

返回

例外

示例

注解

适用于

ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>)

类型参数

参数

返回

例外

注解

适用于

ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>)

类型参数

参数

返回

例外

注解

适用于

ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>)

类型参数

参数

返回

例外

注解

适用于

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